Forced convection oven



Dec. 3, 1968 M. w. MAIER 3,414,708

FORCED CONVECT ION OVEN `Filed Oct. 22, 1965 4 Sheets-Sheet l M. W. MAIER FORCED CONVECTION OVEN Dec. 3, 196s 4 Sheets-Sheet 2 Filed Oct. 22, 1965 FIEL 2 Dec. 3, 1968 M. w. MAIER 3,414,708

FORCED CONVECT ION OVEN Filed Oct. 22, 1965 4 Sheets-Sheet 5 Dec. 3, 1968 M. w. MAIER FORCED CONVECTION OVEN 4 Sheets-Sheet 1 Filed Oct. '21?, 1965 FIEL? United States Patent O 3,414,708 FORCED CONVECTION OVEN Michael W. Maier, Beaver Dam, Wis., assignor to Malleable Iron Range Company, Beaver Dam, Wis., a corporation of Wisconsin Filed Oct. 22, 1965, Ser. No. 500,960 8 Claims. (Cl. 219-400) The present invention relates to improvements in forced convection ovens.

It has previously been proposed to put a fan or blower i in an oven to accelerate the baking process. However,

where the fan is placed at the top or bottom of the oven, the baking pan forms a partial barrier to the air flow within the oven which results in uneven heating of the food being baked. In some cases, as where the air goes up along the side walls of the oven land down in the middie, a crust will be formed at the top of the food, such as a cake, whereas the bottom will be undercooked. In other cases, where the air stream goes up in the middle of the oven and down along the side walls, the bottom of the cake will be overcooked, and the top will be under cooked.

The direction of the air stream is determined by the location of the fan, and by the type, either radial delivery or axial delivery.

In addition, the air stream in the middle of the oven is likely to have a more concentrated heating effect which will cause localized overheating at the area of impingement at the concentrated air stream on the bottom of the pan, in the case of an upwardly directed air stream, or on the top of the food in the pan, in the case of a downwardly directed air stream.

An object of my invention is to provide a more uniform distribution of the air currents in the oven in order that both the top and the bottom of the baking pan will be subjected to the same amount of heat transfer, and in order that localized overheating will be minimized.

According to my invention, the fan is an axial delivery fan, and I provide a ring-shaped baille above the fan, and spaced above the opening in the baille, I provide a second baille in the form of an imperforate disk. The heating element is located at about the same elevation of the fan and surrounds the same, but it is spaced radially from the fan and from the baille assembly by a substantial distance.

According to this arrangement, the air stream is directed upwardly through a hole in the lower baille, and the upper baille serves to direct the air stream radially outward toward the walls of the oven. This arrangement has been found to be very effective in overcoming the diiiiculties encountered in the prior art arrangements, as discussed above.

Another object of my invention is to provide a forced -convection oven in which the fan is protected from overheating even though the oven is operated at relatively high temperatures, as in the case of cooking frozen foods.

A still further object of my invention is to provide an improved forced convection oven in which the fan is located beneath the baking pan where the ambient temperature is lower, and in which means `are provided to protect the fan blades from food drippings.

Other objects, features and advantages will become apparent as the description proceeds.

With reference now to the draw-ings in which like refence numerals designate like parts:

FIG. 1 is a front elevation of an over embodying my invention with a portion of the oven door broken away;

FIG. 2 is a side view of FIG. 1, partially in section;

FIG. 3 is a plan view of the baille assembly;

ice

FIG. 4 is an elevation of FIG. 3, partially in section;

FIG. 5 is a diagram illustrating the operation;

FIG. `6 is an enlarged detail showing the mounting 0f the baille support structure and guard; and

FIG. 7 shows a modification.

The oven shown in FIGS. l and 2 comprises an outer sheet steel casing 10 and an inner casing 11 with insulation material 12 confined within the double wall construction. The insulated double wall construction provide a -top wall 13, a bottom wall 14, two side walls 15, and a back wall 16. A broil unit 17 is located at the top of the oven, and a bake unit 1-8 is located at the bottom of the oven, by means of suitable supports 19. These broil and bake units 18 and 17 are shown as usual rod type electric heating elements although open resistance wires may be used if preferred. The oven thus described is the usual bake and broil combination oven, and one feature of my invention is that the oven is capable of normal baking and broiling use when it is not desired to use the convection fan.

An insulated door 20 is hingedly mounted at the front of the oven in the usual manner.

A compartment 21 is located below the oven for accommodating the usual terminal block, electric cables, and switch mechanisms, not shown. Also located within the compartment 21 is a fan motor 22 having a shaft 23 which extends upwardly through the bottom wall 14. An axial delivery fan 24 is mounted on the shaft 23 at its upper end. The axial delivery fan is surrounded by the bake unit 18 which is of rectangular outline. Above the fan 24 is located a double baille assembly 2S, shown in FIGS. 3 and 4. This vassembly comprises a lower ringshaped baille 26, an upper disk-shaped baille 27 together with a Wire supporting structure 28 for the lower baille 26. Sheet metal spacers 29 mount the upper baille 27 on the lower baille 26. The lower ends of the legs 30 of the supporting structure 28 are secured to the inner casing 11 of the bottom wall 14 in any suitable manner, as by being welded to the interior of a ilanged nut 31 which extends through the inner casing and is welded to the outer surface thereof. This 4avoids damage to the inner surface which may be coated with porcelain enamel.

The fan 24 is rotated in a direction to blow air upwardly and radially outwardly through the throat 32 between the lower and upper bailles 26 and 27.

A sleeve 33 extends through the bottom wall 14 and surrounds the fan shaft 23. This provides a passageway of considerable cross section, `and the rotation of the fan causes air to -be drawn through the sleeve 33 upwardly into the oven. This provides considerable circulation of air through the compartment 21 which cools the fan motor 22.

A small motor cooling fan 34 is secured to a lower extension of the shaft 23 to assure that the air stream passing through the sleeve 33 will pass over the surfaces of the fan motor.

There is sufficient leakage in the sheet metal construction of the switch compartment 21 and also around the oven door to permit the -desired circulation of air; additional vents in the switch compartment may be provided if desired.

It will be noted that the sleeve 33 extends upwardly almost into abutting relationship with the undersurface of the inner casing 11, but does not need to be welded thereto. The inner casing 11 is lprovided with a flanged opening 35, the diameter of which may approximate the diameter of the sleeve 33, or be somewhat smaller as shown.

The sleeve 33 is secured at its lower end to a motor mounting plate 36 which in turn is welded to the undersurface of the outer casing 10, and the body of the motor is secured to the motor mounting plate 36 by suitable bracket means which do not obstruct the ow of air through the sleeve 33.

Air currents substantially as shown in FIG. 2 are observed during the operation of the device, The arrow 40 designates an intake air stream, the arrow 41 an output air stream, arrow 42 a wall-adjacent ascending air stream, and the arrow 43 a vcentrally descending air stream. The customary position for a baking pan is shown by the dotted line 44, that is, interposed in the centrally descending `air stream 43.

It has also been observed that the wall adjacent ascending air stream 42 sweeps across the oven door as indicated by the arrow 42a in FIG. l. In other words, the wall 'adjacent ascending air streams move spirally in the direction of fan rotation.

Preferably, the broil unit 17 is energized at partial heat, and it has been found that this provides more uniform baking of the top of a cake; when not energized, the middle top portion of the cake may be undercooked even though the top is crusted over at the outer top portions.

The exact reason for the improved results is not fully understood. However, it is believed that the arrangement sets up two different air stream paths as diagrammatically indicated in FIG. 5. The primary air stream path A comprises the intake air stream 40 and at least a portion of the output air stream 41. The throat 32 imparts a high velocity to the output air stream 41 and causes it to induce a secondary air stream B, FIG. 5. The secondary air stream comprises the ascending and descending air streams 42 and 43. At the point C where the air stream paths A and B are tangent to each other, heat exchange takes place, probably through commingling.

Thus, the kinetic energy applied to the secondary air stream B is applied throughout a large ring-shaped area C surrounding the baffle assembly 25, making for a what might be termed a diffuse source of energy as compared, for instance, with the blades `of a fan or a blower. Thus, the descending central air stream is also of a diffuse character which permits it to follow all the contours of the baking pan and to bathe the same with an air stream which is less concentrated than, for instance, the

output air stream of an axial delivery fan or the input.

yside -wall as to deflect inwardly a portion of the ascending air stream 42. However, in all arrangements there is a uniform heat transfer at all surfaces of the several baking pans which is believed to be due to the diffuse nature of the induced air streams.

As shown in FIG. 2 the edge 37 of the opening in the lower baffle 26 is located directly above the outer edge of the blades of the fan 24. Hence the lower ring-shaped baflie 26 is disposed in a substantially surrounding relationship with respect to the fan. If preferred, the opening may be Somewhat larger and the elevation of the lower 'baille lowered so that it more nearly coincides with the top edge of the fan blades. In the embodiment shown, the spacing between the upper and lower baffle is substantially three-quarters of an inch, and the diameter of the upper baffle 27 is substantially a quarter of an inch greater than the diameter of the opening in the ringshaped baffle, so that there is a slight overlap. One function of the ring-shaped baille is to separate the intake air stream from the output air stream, and it has been found that the provision of .a relatively narrow throat 4 32 located above the fan is effective to set up the various air streams above described.

In the embodiment shown in FIGS. 1 and 2, the oven is a counter top -oven having legs 45 which maintain the body of the oven spaced above a supporting surface. However, my invention is also applicable to the standard electric range 46, shown in FIG. 7, having surface units 47 and an oven 48 constructed in accordance with the teachings of my invention as illustrated in FIGS. 1 to 6. I have found that any additional heat which may be radiated downwardly by the surface unit 47 does not interfere with the successful operation of the oven, and that the oven ventin-g arrangements which are sometimes provided in electric ranges do not affect the cooperation of the primary and secondary air streams A and B, nor do they materially change the nature of the path of the secondary air stream B. For instance, the structure of one of the surface units 47 constitutes a vent 47a communicating with the oven 48. This facilitates the circulation of air through the switch compartment 21' and the sleeve 33.

As an example of the results obtained with my improved oven, a frozen TV dinner can be brought up from 18 F. to 160 F. in 10` to 12 minutes without preliminary defrosting and without preheating of the oven. With a conventional oven the heating time `is from 25 to 30 minutes plus the time to preheat the oven up to 450 F.

In the baking of a cake, the baking time is cut from 20% to 33%, and the cake is uniformly done at all surfaces.

Although only preferred embodiments of my invention have been shown and described herein, it will be understood that various modifications and changes may be made in the constructions shown without departing from the spirit of my invention as pointed out in the appended claims.

I claim:

1. A forced convection oven comprising an oven enclosure having four walls, a top, and a bottom, an axial delivery fan located near said bottom, a ring-shaped baille located near said fan in substantially surrounding relationship, and au imperforate batile located above the opening in said ring-shaped baffle, said bafes cooperating to direct the output air stream of said fan laterally toward said walls, the intake air stream of said fan moving laterally inward below said ring-shaped bathe, at least a part of said output and input air streams constituting a pirmary air stream path, said output air stream inducing a secondary air stream which moves upwardly along said walls and downwardly in the middle of said oven, and an electric heat source located in said primary air stream path.

2. A forced convection oven as claimed in claim 1 which includes a second heat source located in said secondary air stream.

3. A forced convection oven comprising an oven enclosure having four side walls, a top wall and a bottom Wall, an axial delivery fan localted near said bottom, and a baffle assembly located above said fan, said baffle assembly comprising a ring-shaped bale located slightly above said fan and having an opening of a diameter substantially equal to the diameter of said fan, and an imperforate baiiie located above the opening in said ringshaped baflie, said bales cooperating to direct the output air stream of said fan laterally toward said walls, an electric bake unit surrounding said fan and baffle assembly, and an electric broil unit located at the top of said oven enclosure.

4. A forced convection oven as claimed in claim 3 which includes a compartment located beneath said bottom wall, a sleeve extending through said bottom Wall and providing communication between said compartment and said oven enclosure, a fan motor located in said compartment and having an output shaft extending through said sleeve, said fan being mounted on the upper end of said output shaft, and drawing air upwardly through said sleeve.

S. A forced convection oven as claimed in claim 4 which includes a fan mounted on the lower end of said output shaft beneath said motor, for blowing air upwardly past said motor and toward said sleeve.

6. In a forced convection oven having an insulated bottom wall which includes a sheet metal inner casing having an axial delivery fan located near the bottom of the oven enclosure, the combination of a baille assembly located above said fan and supported on the bottom wall of said oven enclosure, said baille assembly comprising a ringshaped baille having an opening substantially equal to the diameter of said fan, a combined guard and supporting structure therefor surrounding said fan and including downwardly extending legs, a plurality of ilanged nuits secured to the under surface of and extending upwardly through said inner casing, said legs being received within said nuts and welded thereto, and a disk-shaped baille located above the opening in said ring-shaped baille and an electric heat source located in said oven enclosure.

7. An electric range comprising a body having surface units located on the upper surface thereof, an oven 1ocated beneath said surface units, said oven having four side walls, a top wall and a bottom Wall, an axial delivery fan located near said bottom wall, and a baille assembly located above said fan, said baille assembly comprising a ring-shaped baille located slightly above said fan and having an opening of a diameter substantially equal to the diameter of said fan, and a disk-shaped baille located above the opening in said ring-shaped baille, said bailles cooperating to direct the output air stream of said fan laterally toward said side walls, and an electric bake unit surrounding said fan and baille assembly.

8. An electric range as claimed in claim 7 which includes a compartment located beneath said bottom wall, a sleeve extending through said bottom wall and providing communication between said compantment and said oven, a fan motor located in said compartment and having an output shaft extending through said sleeve, said fan being mounted on the upper end of said output shaft and drawing air upwardly through said sleeve, and an oven vent providing communication between said oven and .the atmosphere and facilitating circulation of air through said compartment, past said fan motor, and upwardly through said sleeve.

References Cited UNITED STATES PATENTS 1,986,088 1/1935 Wild 219-400 X 2,408,331 9/ 1946 Mills 219-400 2,957,067 10/1960 Scofield 219-400 3,081,392 3/1963 Warner 219-l0.55 3,118,436 l/1964 Keating 126-19 3,148,674 9/1964 Boardman et al 126--19 3,167,639 1/1965 Gaugler 219--370 FOREIGN PATENTS 755,719 9/1933 France.

1,121,675 5/1956 France.

BERNARD A. GILHEANY, Primary Examiner.

V.'Y. MAYEWSKY, Assistant Examiner. 

1. A FORCED CONVECTION OVEN COMPRISING AN OVEN ENCLOSURE HAVING FOUR WALLS, A TOP, AND A BOTTOM, AN AXIAL DELIVERY FAN LOCATED NEAR SAID BOTTOM, A RING-SHAPED BAFFLE LOCATED NEAR SAID FAN IN SUBSTANTIALLY SURROUNDING RELATIONSHIP, AND IMPERFORATE BAFFLE LOCATED ABOVE THE OPENING IN SAID RING-SHAPED BAFFLE, SAID BAFFLES COOPERATING TO DIRECT THE OUTPUT AIR STREAM OF SAID FAN LATERALLY TOWARD SAID WALLS, THE INTAKE AIR STREAM OF SAID FAN MOVING LATERALLY INWARD BELOW SAID RING-SHAPED BAFFLE, AT LEAST A PART OF SAID OUTPUT AND INPUT AIR STREAMS CONSTITUTING A PIRMARY AIR STREAM PATH, SAID OUTPUT AIR STREAM INDUCING A SECONDARY AIR STREM WHICH MOVES UPWARDLY ALONG SAID WALLS AND DOWNWARDLY IN ATHE MIDDLE OF SAID OVEN, AND AN ELECTRIC HEAT SOURCE LOCATED IN SAID PRIMARY AIR STREAM PATH. 